Japanese non-examined laid-open Patent Publication No. 52-109673 discloses an electric hammer having a vibration reducing device. In the known electric hammer, a vibration proof chamber is integrally formed with a body housing (and a motor housing) in a region on the lower side of the body housing and forward of the motor housing. A dynamic vibration reducer is disposed within the vibration proof chamber. It is designed such that the dynamic vibration reducer reduces a strong vibration which may be caused in the longitudinal direction of the hammer when the hammer is driven
In the above-described dynamic vibration reducer, the weight is disposed under an action of the biasing force of an elastic element. The dynamic vibration reducer performs a vibration reducing function by the weight being driven according to the magnitude of vibration inputted to the dynamic vibration reducer. Specifically, the dynamic vibration reducer has a passive property that the amount of vibration reduction by the dynamic vibration reducer depends on the amount of vibration. In actual operation, a considerable load is applied from the workpiece side to the tool bit, for example, by a user performing the operation while strongly pressing the power tool against the workpiece and therefore, vibration reduction is highly required in such case. However, in some cases, the amount of vibration to be inputted to the dynamic vibration reducer may be reduced.